The present invention relates generally to the field of building pneumatic tires and, more particularly, to a cylindrical drum for building first-stage (raw or uncured), steel-reinforced, radial monoply, pneumatic tire carcasses, whereby a pair of carcass-bead-defining annular metallic cores are secured to the opposite end portions, respectively, of a cylindrically-oriented carcass-ply.
The building drum of the present invention is conventionally characterized as a "shouldered" or "high crown" drum having a substantially cylindrical configuration and terminating at each of its opposite ends in an annular bead-seat having a diameter which is substantially less than the diameter of the cylindrical portion of the drum between the bead-seats. In particular, the drum itself is defined by a circumferential array of drum-forming segments which are radially expansible and contractible, each of the segments having the same axial extent and terminating at each end in a respective flange projecting radially inwardly. Each of the flanges has a respective recess exposed radially outwardly. Corresponding ones of the recesses which are the same segment end define cooperatively with one another at each such segment end a radially outwardly exposed annualar bead-seat.
Such a segmented drum is disclosed in U.S. Pat. No. 3,281,305, issued on Oct. 25, 1966 to H. Nadler, et al. Such a drum is utilized to build first-stage carcasses by contracting the segments radially such that the segments are moved into a minimum diameter-defining disposition. A carcass ply is then wrapped around the drum segments into a cylindrical disposition, the cylindrically-oriented ply having an axial span which at each of its opposite ends extends over and beyond the aforementioned annular bead-seats, respectively. The carcass-ply may overlie an appropriate liner material which is generally coextensive therewith, and may have associated therewith appropriate bead-region filler strips and chafer strips which overlie the opposite end portions thereof in radial alignment with respective ones of the bead-seats.
A pair of carcass-bead-defining annular metallic cores are then disposed concentrically around the drum in radial alignment with respective ones of the bead-seats, each of the annular metallic cores having affixed thereto, in surrounding relation, a respective annular apex strip which is generally triangular in cross-section. The segments are then radially expanded such that the cylindrically-oriented carcass-ply is stretched circumferentially until each of the bead-seats effectively engages a respective one of the annular metallic cores through the intermediary of a respective one of the opposite end portions of the cylindrically oriented carcass-ply. Engagement of the bead-seats with the annular metallic cores, respectively, causes the opposite end portions of the carcass-ply to turn slightly upwardly about the cores and embrace the latter. The end portions of the carcass-ply are then turned upwardly further and "stitched" into adherence with the upper exposed cylindrical surface of the carcass-ply between the annular metallic cores. The drum segments are then contracted once again and the carcass-ply with the annular metallic cores secured to the opposite end portions thereof is removed from th drum in the form of a "first-stage" (raw or uncured) pneumatic tire carcass.
The disadvantage associated with the building drum of the aforementioned Nadler, et al. disclosure is that each of the bead-seats is formed in a respective elastomeric ring which is affixed to and surrounds the circumferential array of drum-forming segments at each of the end portions of the drum. As a result, when the segments are expanded, the elastomeric ring, and consequently the bead-seat-defining annular groove in the elastomeric ring, is caused to stretch both axially and radially, whereby the depth of the annular groove is reduced slightly and the width of the annular groove is increased slightly. The net result is that each of the bead-seats deforms with the expansion and contraction of the drum-forming segments and does not present a distortion-free configuration for turning up and anchoring a respective carcass-ply end portion around a corresponding annular metallic core without distorting the carcass-ply ends themselves. Such distortion often interferes with the quality, and thus utility, of such a carcass.
The problem of bead-region distortion becomes pronounced when building heavy service pneumatic tire carcasses of the steel-reinforced, radial monoply variety for trucks and other large commercial vehicles. The problem is pronounced because of the extreme stiffness of such a radial monoply and the difficulty to neatly turn and anchor (without excessive distortion) the end portions of the monoply around corresponding annular metallic cores and associated apex strips.
Because of the extreme stiffness of the steel-reinforced, radial monoply, and the distortion that each of the bead-seats undergoes in the building drum disclosed in the aforementioned Nadler et al. patent, a drum of such construction is unsuitable for building steel-reinforced, radial monoply, first-stage carcasses. It is just such a disadvantage that the present invention overcomes.